Array ( [0] => {{Short description|Method of combining multiple signals into one signal over a shared medium}} [1] => {{For|multiplexing in electronics and signal processing|Multiplexer}} [2] => {{more footnotes|date=August 2014}} [3] => {{Multiplex techniques}} [4] => [5] => [[File:Multiplexing diagram.svg|thumb|250px|Multiple low [[data rate]] signals are multiplexed over a single high-data-rate link, then demultiplexed at the other end.]] [6] => [7] => In [[telecommunications]] and [[computer network|computer networking]], '''multiplexing''' (sometimes contracted to '''muxing''') is a method by which multiple [[Analog signal|analog]] or [[digital signal]]s are combined into one signal over a [[shared medium]]. The aim is to share a scarce resource {{endash}} a physical [[transmission medium]].{{Citation needed|date=March 2023}} For example, in telecommunications, several [[telephone call]]s may be carried using one wire. Multiplexing originated in [[#Telegraphy|telegraphy]] in the 1870s, and is now widely applied in communications. In [[#Telephony|telephony]], [[George Owen Squier]] is credited with the development of telephone carrier multiplexing in 1910. [8] => [9] => The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end. [10] => [11] => A device that performs the multiplexing is called a [[multiplexer]] (MUX), and a device that performs the reverse process is called a [[demultiplexer]] (DEMUX or DMX). [12] => [13] => [[Inverse multiplexing]] (IMUX) has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate the original data stream. [14] => [15] => In [[computing]], '''I/O multiplexing''' can also be used to refer to the concept of processing multiple [[input/output]] [[Event (computing)|events]] from a single [[event loop]], with system calls like [[poll (Unix)|poll]]{{cite web |author1= Charles M. Hannum |author2= The [[NetBSD]] Foundation |date= 1998 |url= http://bxr.su/n/lib/libc/sys/poll.2 |title= poll, pollts — synchronous I/O multiplexing |website= BSD Cross Reference |publisher= [[NetBSD]]}} and [[select (Unix)]].{{cite web |author1= Computer Systems Research Group |author-link= Computer Systems Research Group |date= 1994 |url= http://bxr.su/n/lib/libc/sys/select.2 |title= select, pselect — synchronous I/O multiplexing |website= BSD Cross Reference |publisher= [[NetBSD]]}} [16] => [17] => ==Types== [18] => Multiple [[variable bit rate]] digital [[bit stream]]s may be transferred efficiently over a single fixed [[Bandwidth (signal processing)|bandwidth]] channel by means of [[statistical multiplexing]]. This is an [[asynchronous serial communication|asynchronous]] mode time-domain multiplexing which is a form of time-division multiplexing. [19] => [20] => Digital bit streams can be transferred over an analog channel by means of code-division multiplexing techniques such as [[frequency-hopping spread spectrum]] (FHSS) and [[direct-sequence spread spectrum]] (DSSS). [21] => [22] => In [[wireless communication]]s, multiplexing can also be accomplished through alternating [[polarization (waves)|polarization]] ([[Horizontal plane|horizontal]]/[[vertical direction|vertical]] or [[clockwise]]/[[counterclockwise]]) on each [[adjacent channel]] and satellite, or through [[phased array|phased multi-antenna array]] combined with a [[multiple-input multiple-output communications]] (MIMO) scheme. [23] => [24] => ===Space-division multiplexing=== [25] => {{Main|Space-division multiple access}} [26] => In wired communication, [[Spatial multiplexing|space-division multiplexing]], also known as space-division multiple access (SDMA) is the use of separate point-to-point electrical conductors for each transmitted channel. Examples include an analogue stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multi-pair [[telephone cable]], a switched [[star network]] such as a telephone access network, a switched Ethernet network, and a [[mesh network]]. [27] => [28] => In wireless communication, space-division multiplexing is achieved with multiple antenna elements forming a [[phased array antenna]]. Examples are [[multiple-input and multiple-output]] (MIMO), single-input and multiple-output (SIMO) and multiple-input and single-output (MISO) multiplexing. An IEEE 802.11g wireless router with ''k'' antennas makes it in principle possible to communicate with ''k'' multiplexed channels, each with a peak bit rate of 54 Mbit/s, thus increasing the total peak bit rate by the factor ''k''. Different antennas would give different [[multi-path propagation]] (echo) signatures, making it possible for [[digital signal processing]] techniques to separate different signals from each other. These techniques may also be utilized for [[space diversity]] (improved robustness to fading) or [[beamforming]] (improved selectivity) rather than multiplexing. [29] => [30] => ===Frequency-division multiplexing=== [31] => [[File:Frequenzmultiplex001.svg|right|thumb|400px|Frequency-division multiplexing (FDM): The spectrum of each input signal is shifted to a distinct frequency range.]] [32] => [[Frequency-division multiplexing]] (FDM) is inherently an analog technology. FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium. '''In FDM the signals are electrical signals.''' [33] => One of the most common applications for FDM is traditional radio and television broadcasting from terrestrial, mobile or satellite stations, or cable television. Only one cable reaches a customer's residential area, but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the appropriate frequency (channel) to access the desired signal.{{citation | title = Voice and Data Communications | first1 = Regis J | first2 = Marcus | last1= Bates| last2 = Bates | year = 2007 | publisher = McGraw-Hill Irwin | isbn = 9780072257328}} [34] => [35] => [[Image:WDM operating principle.svg|400px|thumb|One stream, one color, light waves, in WDM]] [36] => A variant technology, called [[wavelength-division multiplexing]] (WDM) is used in [[optical communication]]s. [37] => [38] => ===Time-division multiplexing=== [39] => [[File:Telephony multiplexer system.gif|right|thumb|400px|Time-division multiplexing (TDM)]] [40] => [[Time-division multiplexing]] (TDM) is a digital (or in rare cases, analog) technology which uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path. [41] => [42] => Consider an application requiring four terminals at an airport to reach a central computer. Each terminal communicated at 2400 [[baud]], so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from the airport ticket desk back to the airline data center are also installed. Some [[Proxy server#Web proxy servers|web proxy servers]] (e.g. [[polipo]]) use TDM in [[HTTP pipelining]] of multiple [[HTTP]] transactions onto the same [[Transmission Control Protocol|TCP/IP connection]].{{cite journal|title = rfc2068 - HTTP/1.1 |year = 1997 |doi = 10.17487/RFC2068 |url = http://tools.ietf.org/html/rfc2068 |access-date = 2010-09-23 |last1 = Fielding |first1 = R. |last2 = Gettys |first2 = J. |last3 = Mogul |first3 = J. |last4 = Frystyk |first4 = H. |last5 = Berners-Lee |first5 = T. }} [43] => [44] => [[Carrier-sense multiple access]] and [[multidrop]] communication methods are similar to time-division multiplexing in that multiple data streams are separated by time on the same medium, but because the signals have separate origins instead of being combined into a single signal, are best viewed as [[channel access method]]s, rather than a form of multiplexing. [45] => [46] => TD is a legacy multiplexing technology still providing the backbone of most National fixed line Telephony networks in Europe, providing the 2m/bit voice and signalling ports on Narrow band Telephone exchanges such as the DMS100. Each E1 or 2m/bit TDM port provides either 30 or 31 speech timeslots in the case of CCITT7 signalling systems and 30 voice channels for customer connected Q931, DASS2, DPNSS, V5 and CASS signalling systems.{{Cite book|title=Breakthroughs in telephone technology: from Bell to smartphones|date=2012|publisher=Britannica Educational |editor=Curley, Robert |isbn=978-1-61530-724-1 |location=New York |page=69|oclc=769190186}} [47] => [48] => ===Polarization-division multiplexing=== [49] => [[Polarization-division multiplexing]] uses the [[polarization (waves)|polarization]] of electromagnetic radiation to separate orthogonal channels. It is in practical use in both radio and optical communications, particularly in 100 Gbit/s per channel [[fiber optic transmission system]]s. [50] => [51] => Differential Cross-Polarized Wireless Communications is a novel method for polarized antenna transmission utilizing a differential technique. {{Citation |title=Differential Cross-Polarized Wireless Communications |author1=Siamack Ghadimi|publisher=Scientific Research|date=2019-04-02}} [52] => [53] => ===Orbital angular momentum multiplexing=== [54] => [[Orbital angular momentum multiplexing]] is a relatively new and experimental technique for multiplexing multiple channels of signals carried using electromagnetic radiation over a single path.{{Cite journal|last1=Tamburini|first1=Fabrizio|last2=Mari|first2=Elettra|last3=Sponselli|first3=Anna|last4=Thidé|first4=Bo|last5=Bianchini|first5=Antonio|last6=Romanato|first6=Filippo|date=2012-01-01|title=Encoding many channels on the same frequency through radio vorticity: first experimental test|url=http://stacks.iop.org/1367-2630/14/i=3/a=033001|journal=New Journal of Physics|language=en|volume=14|issue=3|pages=033001|doi=10.1088/1367-2630/14/3/033001|issn=1367-2630|arxiv=1107.2348|bibcode=2012NJPh...14c3001T|s2cid=3570230}} It can potentially be used in addition to other physical multiplexing methods to greatly expand the transmission capacity of such systems. {{As of|2012}} it is still in its early research phase, with small-scale laboratory demonstrations of bandwidths of up to 2.5 Tbit/s over a single light path.{{cite news|url=https://www.bbc.co.uk/news/science-environment-18551284|title='Twisted light' carries 2.5 terabits of data per second|work=BBC News|date=2012-06-25|access-date=2012-06-25}} This is a controversial subject in the academic community, with many claiming it is not a new method of multiplexing, but rather a special case of space-division multiplexing.{{cite journal|last1=Tamagnone|first1=Michele|last2=Silva|first2=Joana S.|last3=Capdevila|first3=Santiago|last4=Mosig|first4=Juan R.|last5=Perruisseau-Carrier|first5=Julien|title=The orbital angular momentum (OAM) multiplexing controversy: OAM as a subset of MIMO|journal=2015 9th European Conference on Antennas and Propagation (EuCAP)|date=2015|pages=1–5}} [55] => [56] => ===Code-division multiplexing=== [57] => [[Code-division multiplexing]] (CDM), [[code-division multiple access]] (CDMA) or [[spread spectrum]] is a class of techniques where several channels simultaneously share the same [[frequency spectrum]], and this spectral bandwidth is much higher than the bit rate or [[symbol rate]]. One form is frequency hopping, another is direct sequence spread spectrum. In the latter case, each channel transmits its bits as a coded channel-specific sequence of pulses called chips. Number of chips per bit, or chips per symbol, is the [[spreading factor]]. This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber or radio channel or other medium, and asynchronously demultiplexed. Advantages over conventional techniques are that variable bandwidth is possible (just as in [[statistical multiplexing]]), that the wide bandwidth allows poor signal-to-noise ratio according to [[Shannon–Hartley theorem]], and that multi-path propagation in wireless communication can be combated by [[rake receiver]]s. [58] => [59] => A significant application of CDMA is the [[Global Positioning System]] (GPS). [60] => [61] => [[File:telecommunication-multiplexing.svg|thumb|right|400px|Telecommunication multiplexing]] [62] => [63] => ==Multiple access method== [64] => A multiplexing technique may be further extended into a [[multiple access method]] or [[channel access method]], for example, TDM into [[time-division multiple access]] (TDMA) and statistical multiplexing into [[carrier-sense multiple access]] (CSMA). A multiple access method makes it possible for several transmitters connected to the same physical medium to share its capacity. [65] => [66] => Multiplexing is provided by the [[Physical layer|Physical Layer]] of the [[OSI model]], while multiple access also involves a [[media access control]] protocol, which is part of the [[data link layer|Data Link Layer]]. [67] => [68] => The Transport layer in the OSI model, as well as TCP/IP model, provides statistical multiplexing of several application layer data flows to/from the same computer. [69] => [70] => [[Code-division multiplexing]] (CDM) is a technique in which each channel transmits its bits as a coded channel-specific sequence of pulses. This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplexed. Other widely used multiple access techniques are [[time-division multiple access]] (TDMA) and [[frequency-division multiple access]] (FDMA). [71] => Code-division multiplex techniques are used as an access technology, namely code-division multiple access (CDMA), in Universal Mobile Telecommunications System (UMTS) standard for the third-generation (3G) mobile communication identified by the ITU.{{citation needed|date=June 2018}} [72] => [73] => ==Application areas== [74] => [75] => ===Telegraphy=== [76] => The earliest communication technology using electrical wires, and therefore sharing an interest in the economies afforded by multiplexing, was the [[electric telegraph]]. Early experiments allowed two separate messages to travel in opposite directions simultaneously, first using an electric battery at both ends, then at only one end. [77] => [78] => [[Émile Baudot]] developed a [[time-multiplexing]] system of multiple [[David E. Hughes|Hughes]] machines in the 1870s. In 1874, the [[quadruplex telegraph]] developed by [[Thomas Edison]] transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time. Several researchers were investigating [[acoustic telegraphy]], a [[frequency-division multiplexing]] technique, which led to the [[invention of the telephone]]. [79] => [80] => ===Telephony=== [81] => In [[telephony]], a [[customer]]'s [[local loop|telephone line]] now typically ends at the [[remote concentrator]] box, where it is multiplexed along with other [[telephone line]]s for that [[neighborhood]] or other similar area. The multiplexed signal is then carried to the [[telephone exchange|central switching office]] on significantly fewer wires and for much further distances than a customer's line can practically go. This is likewise also true for [[digital subscriber line]]s (DSL). [82] => [83] => [[Fiber in the loop]] (FITL) is a common method of multiplexing, which uses [[optical fiber]] as the [[Backbone network|backbone]]. It not only connects [[Plain old telephone service|POTS]] phone lines with the rest of the [[PSTN]], but also replaces DSL by connecting directly to [[Ethernet]] wired into the [[home]]. [[Asynchronous Transfer Mode]] is often the [[communications protocol]] used.{{citation needed|date=June 2018}} [84] => [85] => [[Cable TV]] has long carried multiplexed [[television channel]]s, and late in the 20th century began offering the same services as [[telephone companies]]. [[IPTV]] also depends on multiplexing. [86] => [87] => ===Video processing=== [88] => {{Main|Demultiplexer (media file)}} [89] => In [[video]] editing and processing systems, multiplexing refers to the process of interleaving audio and video into one coherent data stream. [90] => [91] => In [[digital video]], such a transport stream is normally a feature of a [[container format (digital)|container format]] which may include [[metadata]] and other information, such as [[subtitle (captioning)|subtitles]]. The audio and video streams may have variable bit rate. Software that produces such a transport stream and/or container is commonly called a multiplexer or '''muxer'''. A '''demuxer''' is software that extracts or otherwise makes available for separate processing the components of such a stream or container. [92] => [93] => ===Digital broadcasting=== [94] => In [[digital television]] systems, several variable bit-rate data streams are multiplexed together to a fixed bit rate transport stream by means of [[statistical multiplexing]]. This makes it possible to transfer several video and audio channels simultaneously over the same frequency channel, together with various services. This may involve several [[standard-definition television]] (SDTV) programmes (particularly on [[DVB-T]], [[DVB-S2]], [[ISDB]] and ATSC-C), or one [[HDTV]], possibly with a single SDTV companion channel over one 6 to 8 MHz-wide TV channel. The device that accomplishes this is called a [[statistical multiplexer]]. In several of these systems, the multiplexing results in an [[MPEG transport stream]]. The newer DVB standards DVB-S2 and [[DVB-T2]] has the capacity to carry several [[HDTV]] channels in one multiplex.{{citation needed|date=June 2018}} [95] => [96] => In [[digital radio]], a multiplex (also known as an ensemble) is a number of radio stations that are grouped together. A multiplex is a stream of digital information that includes audio and other data.{{cite web|url=https://www.radioandtvhelp.co.uk/interference/rtis_radio/DABmuxes_DABradio|title=All about DAB multiplexes|work=Radio & Television Investigation Service|publisher=[[BBC]]|access-date=17 June 2018}} [97] => [98] => On [[communications satellite]]s which carry [[Broadcasting|broadcast]] [[television network]]s and [[radio network]]s, this is known as '''multiple channel per carrier''' or '''MCPC'''. Where multiplexing is not practical (such as where there are different sources using a single [[transponder]]), [[single channel per carrier]] mode is used.{{citation needed|date=June 2018}} [99] => [100] => ===Analog broadcasting=== [101] => In [[FM broadcasting]] and other [[analog signal|analog]] [[radio]] media, multiplexing is a term commonly given to the process of adding [[subcarrier]]s to the audio signal before it enters the [[transmitter]], where [[modulation]] occurs. (In fact, the stereo multiplex signal can be generated using time-division multiplexing, by switching between the two (left channel and right channel) input signals at an ultrasonic rate (the subcarrier), and then filtering out the higher harmonics.) Multiplexing in this sense is sometimes known as '''MPX''', which in turn is also an old term for [[stereophonic]] FM, seen on [[stereo system]]s since the 1960s. [102] => [103] => ==Other meanings== [104] => In [[spectroscopy]] the term is used to indicate that the experiment is performed with a mixture of frequencies at once and their respective response unravelled afterwards using the [[Fourier transform]] principle. [105] => [106] => In [[computer programming]], it may refer to using a single in-memory resource (such as a file handle) to handle multiple external resources (such as on-disk files).{{cite web [107] => | title = Multiplexing filehandles with select() in perl [108] => | url = http://www.perlfect.com/articles/select.shtml}} [109] => [110] => [111] => Some electrical multiplexing techniques do not require a physical "[[multiplexer]]" device, they refer to a "[[keyboard matrix (music)|keyboard matrix]]" or "[[Charlieplexing]]" design style: [112] => * Multiplexing may refer to the design of a [[multiplexed display]] (non-multiplexed displays are immune to [[multiplexed display#"Break up"|break up]]). [113] => * Multiplexing may refer to the design of a "switch matrix" (non-multiplexed buttons are immune to "phantom keys" and also immune to [[Keyboard (computing)#Control processor|"phantom key blocking"]]). [114] => [115] => In high-throughput [[DNA sequencing]], the term is used to indicate that some artificial sequences (often called ''barcodes'' or ''indexes'') have been added to link given sequence reads to a given sample, and thus allow for the sequencing of multiple samples in the same reaction. [116] => [117] => In [[sociolinguistics]], multiplexity is used to describe the number of distinct connections between individuals who are part of a [[social network (sociolinguistics)|social network]]. A multiplex network is one in which members share a number of ties stemming from more than one social context, such as workmates, neighbors, or relatives. [118] => [119] => ==See also== [120] => {{Portal|Electronics}} [121] => * [[Add-drop multiplexer]] [122] => * [[Central office multiplexing]] [123] => * [[Channel bank]] [124] => * [[Multiplexed display]] [125] => * [[Optical add-drop multiplexer]] [126] => * [[Orthogonal frequency-division multiplexing]] (OFDM) (which is a modulation method) [127] => * [[Statistical multiplexing]] [128] => [129] => ==References== [130] => {{Reflist}} [131] => {{Refbegin}} [132] => *{{cite web |url=http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |title=Federal Standard 1037C: Glossary of Telecommunications Terms |publisher=Institute for Telecommunication Services |access-date=2009-10-19 |archive-date=2009-03-02 |archive-url=https://web.archive.org/web/20090302235918/http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |url-status=dead }} [133] => {{Refend}} [134] => * [https://doi.org/10.1117/12.2569003 Efficient beam multiplexing using a spatial light modulator] [135] => [136] => ==External links== [137] => *{{Wiktionary-inline|multiplexing}} [138] => *{{Commons category-inline}} [139] => [140] => {{Telecommunications|state=closed}} [141] => [142] => [[Category:Multiplexing| ]] [143] => [[Category:Digital television]] [144] => [[Category:Digital radio]] [145] => [[Category:Broadcast engineering]] [146] => [[Category:Physical layer protocols]] [147] => [[Category:Television terminology]] [] => )
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Multiplexing

Multiplexing is a technique used in telecommunications and computer networks to combine multiple data signals and transmit them over a single communication channel. It allows multiple users or data streams to share the same transmission medium, thereby optimizing the use of available bandwidth and improving overall efficiency.

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It allows multiple users or data streams to share the same transmission medium, thereby optimizing the use of available bandwidth and improving overall efficiency. There are several types of multiplexing, including time-division multiplexing (TDM), frequency-division multiplexing (FDM), and code-division multiplexing (CDM). In TDM, different signals are divided into time slots and transmitted sequentially, while FDM involves dividing the available frequency range into multiple non-overlapping frequency bands for simultaneous transmission of different signals. CDM, on the other hand, assigns a unique code to each signal and transmits them simultaneously by modulating the codes. Multiplexing is widely used in various communication systems, such as telephone networks, cable television, satellite communication, and computer networks. It allows for efficient transmission of voice, data, and video signals, enabling a higher capacity and improved quality of service. The Wikipedia page on multiplexing provides detailed information about the different types of multiplexing techniques, their applications, advantages, and disadvantages. It also discusses the historical development of multiplexing and its significance in modern communication systems. Additionally, the page covers related topics, such as demultiplexing, multiplexers, and multiplexing protocols. Overall, the Wikipedia page on multiplexing serves as a comprehensive resource for understanding the concept and applications of multiplexing in telecommunications and computer networks.

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